Female gametophyte in angiosperms. Female gametophyte in angiosperm is eight nucleate. 2022-10-06
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The female gametophyte, also known as the megagametophyte or the embryo sac, is an important part of the reproductive process in angiosperms, or flowering plants. It is responsible for the production and nourishment of the female gamete, or egg cell, and plays a crucial role in the fertilization of the plant.
The female gametophyte is typically much smaller than the male gametophyte, or pollen grain, and is located within the ovule, which is contained within the ovary of the flower. The ovary is the female reproductive structure of the flower, and it contains the ovules, which are the structures that will eventually develop into seeds once fertilization has occurred.
The female gametophyte begins to develop within the ovule as a single cell, which then divides to form a multicellular structure known as the prothallus. The prothallus contains the female gamete, or egg cell, as well as several other cell types that will eventually develop into the various tissues of the developing seed.
Once the prothallus has developed, it is ready to receive the male gametophyte, or pollen grain, which carries the male gamete, or sperm cell. Pollination occurs when the pollen grain lands on the stigma, the sticky surface at the top of the pistil, which is the female reproductive structure of the flower. The pollen grain then germinates and grows a pollen tube down through the pistil, which carries the sperm cells to the ovule where fertilization can occur.
Once fertilization has occurred, the female gametophyte begins to develop into the seed, which will eventually contain the embryo plant and the endosperm, a tissue that provides nourishment to the developing plant. The seed will also be surrounded by a seed coat, which helps protect the developing plant and enables it to disperse and germinate in new locations.
In conclusion, the female gametophyte plays a crucial role in the reproductive process of angiosperms, producing and nourishing the female gamete and facilitating fertilization. It is a key component of the plant's reproductive system, and its development into the seed is essential for the continuation of the plant species.
After fertilization, the ovule gives rise to a seed; the seed's embryo, endosperm, and seed coat are derived from the fertilized egg cell, fertilized central cell, and ovule integuments, respectively The female gametophyte plays a critical role in essentially every step of the reproductive process. The nuclei themselves may serve as microtubule-organizing centers and may determine the deposition of cell wall material. Gametophytic mutants typically are identified using two criteria: reduced seed set and segregation distortion. Megaspore mother cell identity is determined by genetic and epigenetic processes, which limit megaspore mother cell production to a single cell per ovule. Female gametophyte development begins with the creation of a diploid megaspore mother cell that undergoes meiosis early in ovule development. The nucleus of the lower divides to form 2, 4 and then 8 nuclei, which give rise to an embryo sac with the usual organization.
Callose accumulates around the three abortive megaspores and, as a result, plasmodesmata are not established around these cells and they subsequently undergo apoptosis. Angiosperms have two types of fertilisation. However, we still know little about pollen tube guidance, fertilization, and the maternal control of seed development at the molecular level. Schematic of female gametophyte initiation and development within the Arabidopsis ovule. After Friedman and Williams, 2004. The development of in vitro fertilization systems An alternative approach is the identification of mutants defective in the fertilization process. Second, gfa2 and srn embryo sacs fail to undergo synergid cell death and yet attract pollen tubes, suggesting that synergid cell death is not required for pollen tube attraction.
Choose the following option which represents the female gametophyte of angiosperm.
Usually, only one tube develops from a pollen grain. As a consequence, gametophytic mutations exhibit non-Mendelian segregation patterns and can only be transmitted from generation to generation as heterozygotes. Note that this female gametophyte type is identical to the Oenothera type of Figure 11. Penea type Stephens 1909 described an interesting mode of development in three genera of the Penaeaceae, viz. Interestingly, all three genes encode components of the RNA splicing machinery. The megaspore mother cell goes through meiosis to produce four haploid offspring. Plumbago type The embryo sac of Plumbago capensis, described by Haupt 1934 , may be presented as a representative of the Plumbago type.
From these studies, we are beginning to understand the regulatory networks involved in female gametophyte development and function. This comes about in a very peculiar manner. In plants, DNA methylation, histone modifications, ATP-dependent chromatin remodeling, placement of histone variants, and noncoding RNA regulation play critically important roles in regulating gene expression. These data suggest that synergid cell death requires functional mitochondria, which also are required for cell death in animals FER and SRN are unknown. Initially, the megaspore undergoes one or more rounds of mitosis without cytokinesis, resulting in a multinucleate coenocyte. By contrast, in other species, including Arabidopsis, synergid degeneration is not an inherent feature of the megagametogenesis process per se, because synergid cell death does not occur if pollination is prevented Because fertilization takes place within the embryo sac, it is likely that many female gametophyte—expressed gene products are necessary for this process. CKI1 can induce a cytokinin response via the AHPs independently of AHK function.
The megaspore traverses a polygonum-type pathway in most flowering plant species, including Arabidopsis and maize, resulting in a seven-celled female gametophyte. Angiosperms have both female and male gametophytes. However, subsequent experimental data and theoretical modeling did not support such a model Ceccato et al. For example, with FIS2 and MEA, the maternal alleles are active but the paternal alleles are inactive during endosperm development The imprinting is achieved via epigenetic modification of the maternal or paternal alleles, a process generally associated with the methylation of cytosine residues within and flanking the coding region of the target gene MEA gene. Carmichael, in Encyclopedia of Applied Plant Sciences, 2003 Female Gametophyte Development Development of the embryo sac female gametophyte takes place in tissues embedded within the ovule.
Female Gametophyte: The Embryo Sac with Its Types : Plantlet
Here the 16 nuclei lie in four distinct quarters which are arranged crosswise, one at each end of the embryo sac and two at the sides. Minimum monthly resolution - Publish 1 , Revise 3 , Share 5. In addition, a comprehensive profile of the genes expressed in the female gametophyte has not been obtained. This haploid megaspore nucleus then divides mitotically to yield two nuclei, each of those two nuclei divide to yield four, and each of those four divide to yield eight. In time-limited habitats, short lifecycles are commonly associated with an annual habit, shorter bud development time, and reduced flower longevity i. Pollen Tube Guidance During the final stages of pollen tube growth, the pollen tube grows toward an ovule and then up the surface of the funiculus until it enters the micropyle to penetrate the female gametophyte To determine whether the female gametophyte plays a role in pollen tube guidance, several groups analyzed pollen tube growth patterns in Arabidopsis mutants defective in embryo sac development.
Female gametophyte in angiosperm is eight nucleate.
Apogamy involving an unfertilized egg a phenomenon termed In certain species of. These are, endospory and an extreme reduction of mitotic cell divisions prior to segregation of the male germline sensu stricto, increased sporophytic dependency, and adaptation to a siphonogamous gamete delivery system involving the loss of gamete motility. Thus, a mature anther shows 3 different wall layers around each sporangium. The female gametophyte is the embryo sac, while the male gametophytes are pollen grains. In rice, a different ARGONAUTE gene, called MEIOSIS ARRESTED AT LEPTOTENE1 MEL1 , has been found to be required for progression of the MMC through meiosis, although the precise mechanism is unclear Nonomura et al.
Formation and development of male and female gametophytes in angiosperms
Of the remaining 7 nuclei, 4 presumably one member of each of the original four pairs undergo a slight increase in size and gradually approach one another, functioning as polar nuclei. Similarly, the megaspore mother cell, apomictic initial cell, egg cell, aposporous initial cell, synergids, and central cell in the female gametogenesis process have been used to develop cell type-specific omics data sets in Arabidopsis, rice, and other plant species Schmid et al. In the wild type, PHE1 expression occurs in the early stages of endosperm development and is not detected in the female gametophyte before fertilization. Furthermore, improved cell biological approaches did not provide evidence for auxin accumulation in the female gametophyte. Female gametophyte stages FG1—FG7 showing the sequence of syncitial mitotic divisions that lead to cellularization and formation of the seven-cell eightnucleate embryo sac at FG6. Furthermore, the cell walls of the egg, synergid, and central cells are missing or discontinuous in the locations where they intersect, and the plasma membranes of these cells are in direct contact with one another. Megasporogenesis occurs when diploid megaspore mother cells conduct meiosis and produce haploid megaspores, which then mature into haploid female gametophytes during megagametogenesis.
The female gametophyte is critical to many steps of the angiosperm reproductive process, including pollen tube guidance, fertilization, the induction of seed development upon fertilization, and maternal control of seed development after fertilization. The female gametophyte FG develops within the ovule, the male gametophyte MG within the anther primordia. The synergids play an important role in fertilization by attracting pollen tubes toward the embryo sac and facilitating the fertilization process see below. Chromatin immunoprecipitation assays have shown that MEA and FIE interact directly with the PHE1 promoter. Double fertilization enhances the fitness of the embryo, but also contributes to maternal fitness, as resources are only committed to the ovule after the egg and central cell have been fertilized. The particular type of megagametogenesis is a function of mitotic divisions, the formation of new cells, and the fusion of existing nuclei or cells.
In fact, female gametophyte development is not only sustained by redundant gene functions but also by redundant cellular functions, which are encoded by accessory cells that can become gametically active in case of gametic failure. The basal region of the ovule, where the funicle remains attached is called chalaza. Sporophytic mutations affect the diploid sporophyte phase of the plant life cycle and exhibit Mendelian 1:2:1 segregation patterns. Sporophytic mutations that affect these processes are identified in screens for female-sterile mutants Gametophytic mutations affect those aspects of female gametophyte development that occur after meiosis, including megagametogenesis and functioning of the mature female gametophyte pollen tube guidance, fertilization, induction of seed development, or maternal control of seed development. Fritillaria type Following the work of Treub and Mellink 1880 on Lilium bulbiferum, several other investigators, notably Strasburger, Mottier, Guignard, Coulter, and Sargant, studied a number of species of this genus and repeatedly confirmed that the 4 megaspore nuclei undergo only one division to give rise to the 8 nuclei of the mature embryo sac. This egg apparatus consists of two lateral synergids and a median large egg cell or ovum or female gamete.